Czech J. Food Sci.
Vol. 19, No. 2: 73–80
Application of Electrodialysis for Lactic Acid Recovery
1
1
1
1
2
VÌRA HÁBOVÁ , KAREL MELZOCH , MOJMÍR RYCHTERA , LIBOR PØIBYL and VLADIMÍR MEJTA
1
Institute of Chemical Technology, Prague – Department of Fermentation Chemistry and Bioengi2
neering and Department of Inorganic Technology, Prague, Czech Republic
Abstract
HÁBOVÁ V., MELZOCH K., RYCHTERA M., PØIBYL L., MEJTA V. (2001): Application of electrodialysis for lactic acid
recovery. Czech J. Food Sci., 19: 73–80.
The paper deals with the possibility of using two-stage electrodialysis for recovery of lactic acid from model solutions and from
fermentation broth. In the first step lactate was concentrated with desalting electrodialysis using ion exchange membranes Ralex
(Mega, Czech Republic). The highest final concentration of 111 g/l was reached in the concentrate, it means an increase more than
2.5-times in comparison with the initial concentration. At the most 2 g of lactate per litre remained in the feed. The second step
was the electroconversion of sodium lactate to lactic acid by water-splitting electrodialysis with the bipolar membranes Neosepta
(Tokuyama Corp., Japan). The final lactic acid concentration of 157 g/l was reached in the diluate. Total required energy in both
electrodialysis processes consisting of the energy consumption for lactate transfer and for its electroconversion to lactic acid was
142 Wh/mol. The fermentation broth was decolourised before electrodialysis experiments. The best decolourisation capacity was
shown by granulated active charcoal filled in the column operated by a slow flow of broth.
Keywords: lactic acid recovery; electrodialysis; desalting electrodialysis; water-splitting electrodialysis; decolourisation
Lactic acid is one of the organic acids having wide use
in many fields, e.g. food industry, beverage industry, pharmaceutical industry, chemical industry, medicine (VICK
ROY 1985). Today, two thirds of the world production of
lactic acid are manufactured by the fermentation method
(KAŠÈÁK et al.1996). The conventional fermentation process produces calcium lactate precipitate, which must be
concentrated by evaporation and reacidified with strong
acid (BUCHTA et al. 1983). The disadvantages of the conventional fermentation process are low reaction rate, elaborate product recovery, large amount of by-products and
thereby negative impacts on the environment. There are
other possibilities for lactic acid recovery, but solvent
extraction, direct distillation, adsorption and other relatively simple methods have some limitations that obstruct
their wider use (LEE et al. 1998; HERIBAN et al. 1993).
Electrodialysis is one of the very promising and perspective methods conditioned by rapid development of the
membrane processes, especially the membranes in the 80’s
and 90’s (ASENJO 1990).
Electrodialysis is a process where ion exchange membranes are used for removing ions from an aqueous solution under the driving force of electrical potential.
Electrodialysis is applied to remove salts from solutions
or to concentrate ionic substances. A large number of
existing applications of electrodialysis was described in
the literature (BLEHA et al. 1988; KRAVJAROVÁ 1991;
MATEUS et al. 1993). A special type of electrodialysis is
water-splitting electrodialysis. Instead of anion exchange
membranes in desalting, bipolar membranes are used in
water-splitting electrodialysis. Bipolar membranes are
composed of anion and cation exchange layers. Water is
split to H+ and OH– ions in the interlayer, which is formed
by water film. Ions pass through the corresponding layer
of the membrane. Water-splitting electrodialysis is applied
to electroconversion of salts to the corresponding acids
(MULDER et al. 1991).
There are two different methods for recovery of lactic
acid. It is a two-stage electrodialysis method in the first
case and electrodialysis with double exchange reaction in
the second case. The two-stage electrodialysis method
was described by GLASSNER and DATTO (1990). In the
first step of desalting, sodium lactate is recovered, purified and concentrated, in the water-splitting or acidification step, lactic acid is regenerated from sodium lactate,
and sodium hydroxide is recovered and purified. In the
The work was supported by EUREKA Σ! 1820 BIOLACTATE and grant No. CEZ:J19/98: 223300005 of the Ministry of Education, Youth and Sport.
73
Vol. 19, No. 2: 73–80
first step sodium lactate is pumped through the diluate
circuit. When a direct current is applied, the positively
charged sodium ions migrate to the cathode and pass
through cation exchange membranes to the concentrate
being accumulated there. The negatively charged lactate
ions migrate to the anode and pass through anion exchange membranes to the concentrate. They are accumulated in the concentrate, too. The concentration of sodium
lactate in the concentrate gradually increases. In the second step, the concentrated sodium lactate solution is
pumped into the diluate cells, where it is converted to
lactic acid by H+ ions arising by water-splitting. Na+ ions
are pushed out through the cation exchange membranes
to the concentrate, where they combine with OH- ions to
sodium hydroxide. LEE et al. (1998) studied the two-stage
electrodialysis method for lactic acid recovery. In the desalting electrodialysis, 115 g lactate per litre was obtained
in the concentrate, only 1g lactate per litre remained in the
diluate, the current efficiency was about 90% and the energy consumption for lactate transfer from diluate to concentrate was 0.25 kWh/kg. In the second step, 88–93% of
the total amount of lactate was converted to lactic acid,
the current efficiency was about 80%. The total energy
consumption for lactic acid recovery was in the range
from 0.78 to 0.97 kWh/kg.
Electrodialysis with double exchange reaction represents the second method. It is a one-step process. The
processed lactate solution and the mineral acid solution
(e.g. H3PO4) are pumped into the diluate streams. There
are two outlets, the first for the salt of mineral acid and the
second for lactic acid. HERIBAN et al. (1993) reached 4times higher lactic acid concentration in the continuous
mode compared to the lactic acid concentration in the
processed solution. 236.8 g lactic acid per litre was obtained in the course of experiment with model solutions,
the energy consumption was in the range from 1.3 to
2.3 kWh/kg.
An advantage of the electrodialysis is a possibility to
be coupled directly with fermentation. HONGO et al. (1986)
proposed to use electrodialysis for in situ lactate recovery to reduce the product inhibition. The obtained productivity was three times higher than in non-pH controlled
fermentation. However, the fouling of anion-exchange
membranes by cells was observed in electrodialysis fermentation. To solve this problem, NOMURA et
al. (1987) used immobilized growing cells entrapped in
calcium alginate. The amount of lactic acid produced by
semicontinuous electrodialysis fermentation using immobilized cells was 8-times higher than that produced by
non-pH controlled fermentation, but some free cells were
determined in the solution. CZYTKO et al. (1987) found
out that the electrodialysis unit could only be operated
with cell free solutions in order to prevent deposition of
bacteria on the membrane surface and creation of bacteria
clusters in the spacer between the membranes. To increase
74
Czech J. Food Sci.
the productivity of the lactic acid fermentation and to
reduce the amounts of effluents, BOYAVAL et al. (1987)
chose for the lactic acid fermentation the bioreactor with
total cell recycling, which was coupled with an ultrafiltration module and an electrodialysis unit, the outlet concentration of lactate was stabilized at 85 g/l. A similar
system was studied by YAO and TODA (1990), H2SO4 was
used as a donor of protons and lactic acid was the final
product, its concentration reached 90 g/l.
MATERIAL AND METHODS
Chemicals: Sodium lactate (p. a. purity) was from Sigma, the other chemicals were chemically pure products of
Lachema (Brno, Czech Republic). Demineralised water was
prepared from distilled water in a device Millipore – Q
gradient 18.2 MΩ.cm (Molsheim, France). Real fermentation broth was obtained from the continuous lactic acid
fermentation with recycle using Lactobacillus plantarum
L10 as a producer strain (SVOBODOVÁ 1999). Lactate concentration ranged from 17 to 22 g/l. Granulated active charcoal and non-ionogenic sorbent Amberlite XAD 4
(Supelco, Switzerland) were used as agents for decolourisation of fermentation broth.
Analytical Methods: Lactate, citrate, acetate and glucose were determined by HPLC (Laboratorní pøístroje Prague, Czech Republic); column – Ostion LG KS in H-cycle;
refractometer detector RIDK 101; mobile phase – H2SO4
(c = 0.005 mol/l), flow rate of mobile phase 0.5 ml/min; column temperature 85° C. The concentration of lactic acid
and the concentration of NaOH were titrated by standard
solution of NaOH (c = 0.025 mol/l), resp. HCl (c = 1 mol/l),
using phenolphthalein as indicator. The colour of fermentation broth was measured by spectrophotometer at wavelength of 400 nm relative to water.
Electrodialysis Equipment: Electrodialysis laboratory
unit BEL-500 (Berghof, Germany) consisted of control unit
(adjustable outputs of voltage from 0 to 50 V and current
from 0 to 3.9 A), measuring device (conductivity and voltage) and 3 independent circulation circuits with pumps
and storage containers (for the diluate, the concentrate
and the electrode solution). The membrane stack Type
500 (Berghof, Germany) and membrane stack ED 0 (Mega,
Czech Republic) with 5 and/or 20 pairs of ion-exchange
membranes Ralex CMH and Ralex AMH were used for the
desalting electrodialysis experiments, their effective membrane areas were 58 cm2 (Type 500) and 180 cm2 (ED 0).
Stack Type 500 with 4 bipolar membranes Neosepta BP-1
and 5 cation exchange membranes Neosepta CMB
(Tokuyama Corp., Japan) were used for water-splitting
electrodialysis.
Limiting Current Measurements: To maintain the constant lactate concentration, the diluate and concentrate
circuits were connected. The relationship between voltage and current was measured for different concentra-
Czech J. Food Sci.
Vol. 19, No. 2: 73–80
tions of sodium lactate. The limiting current for each lactate concentration was identified from a graph.
Operating Conditions – Desalting Electrodialysis:
Electrodialysis experiments were carried out in a batch
mode. The electrode solution (Na2SO4 – 25 g/l), the concentrate (sodium lactate – initial concentration 4 g/l) and
the diluate (sodium lactate – initial concentration from 15
to 42 g/l) were circulated through the corresponding compartments of the desalting stack with flow 60–70 l/h. For
the constant current period, voltage 1.5 V per one pair
and current 1.4 A were used for both stacks. For the constant voltage period, voltage 12V and 16 V were used for
stack Type 500 and stack ED 0, respectively. The experiments were terminated when the lactate concentration in
the diluate dropped to 1–2 g/l.
Operating Conditions – Water-splitting Electrodialysis: The following solutions were used: NaOH – 20 g/l
(electrode solution), NaOH – 1g/l (concentrate), sodium
lactate 43 and 178 g/l (diluate). Current 3.9 A and voltage
12 V were applied. When the conductivity in the diluate
reached the value 5 mS/cm, the experiment was terminated.
Decolourisation: Decolourisation was carried out in the
glass column filled with the above-mentioned material (bed
volume 40 ml), the flow rate of the fermentation broth
through the column was from 40 to 300 ml/h. The fermentation broth was filtrated through the microfilter before
decolourising.
Calculations: The calculation equations were taken from
LEE et al. (1998) and JANDOVÁ (1996).
RESULTS AND DISCUSSION
Desalting Electrodialysis
The initial measurements were focused on determination of the conditions for electrodialysis experiments, first
of all on limiting current measurements for both membrane
stacks. The limiting current is the maximum current for a
given bulk lactate concentration, further current increase
does not promote the ion transport rate any more, only
the electrical resistance increases rapidly. The excessive
energy is also dissipated for splitting water and the current efficiency significantly decreases. If the operating
current is beyond the limiting value, the membranes can
irreversibly be damaged. The method of limiting current
determination is evident from Fig. 1. It has been found
that the limiting current depends on the lactate concentration, limiting current increases with the increasing lactate concentration. The maximum limiting currents 1.51 A
(for stack Type 500) and 1.58 A (for stack ED 0) were
found with the lactate concentration 16 g/l and 6.5 g/l,
respectively (Fig. 2). The limiting current was not found
at higher lactate concentrations than those mentioned
above. The working currents were a bit lower than the
determined maximal limiting currents to prevent the operation beyond the limiting current. For the constant-current period, the current 1.4 A was used for both stacks.
When the lactate concentration decreased to the limiting
value, the operating mode was switched from the constant-current mode to the constant-voltage mode and
voltages of 16 V and 12 V were adjusted for stack ED 0
and Type 500, respectively. The characteristic course of
the electrodialysis experiment is illustrated in Fig. 3. The
results of the performed experiments are shown in Table
1. The experiments DS 1–DS 3 were carried out with the
aim of considering the influence of the applied current on
the course of electrodialysis. It was found that the current value significantly influenced the transport rate of
lactate ions through the membrane. A decrease in current
from 1.4 A to1.0 A resulted in the prolongation of constant-current period by 90 min, that means by 60%, and in
the significantly decreased rate of the lactate transport
(Table 1 – experiments DS 3 and DS 1), therefore all other
experiments were performed at current 1.4 A. The value of
the lactate concentration in the concentrate is very important for the next recovery step, i.e. for electroconversion. The degree of concentration (the ratio of final
concentrate concentration to initial diluate concentration)
can be influenced by a change in the ratio of initial diluate
volume to initial concentrate volume (Fig.4). However, the
2.0
25
Current (A)
Resistance ( )
30
20
15
10
1.5
1.0
0.5
5
limiting current
0.0
Ü
0
0
2
4
6
8
10
1/Current (1/A)
Fig. 1. Identification of the limiting current (membrane stack Type
500, lactate concentration = 7 g/l, limiting current = 0.84 A)
0
5
10
15
20
Lactate concentration (g/l)
Fig. 2. The dependence of the limiting current on the lactate
concentration (membrane stack Type 500)
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Vol. 19, No. 2: 73–80
Czech J. Food Sci.
15
1.0
10
Voltage
0.5
5
Current
Conductivity
0
0
Lactate concentration (g/l
Fig. 3. The time course of the desalting electrodialysis experiment (membrane stack
Type 500, experiment DS 3)
1.5
Current (A)
Conductivity (mS/cm)
Voltage (V)
20
50
100
150
200
0.0
300
Time (min)
250
40
Concentrate
30
20
10
Diluate
0
0
50
100
150
200
250
300
Time (min)
3.0
Fig. 4. Ratio of the final concentrate concentration to
the initial diluate concentration (axis x) vs. ratio of the
initial diluate volume to the initial concentrate volume (axis y)
2.0
1.0
0.0
0.0
2.0
4.0
6.0
Conductivity (mS/cm)
Voltage (V)
1.2
20
Current (A)
1.6
30
Voltage 0.8
Current
10
0.4
Conductivity
0
0
0
60
120
180
240
300
360
420
480
Time (min)
60
Concentrate
Concentration (g/l)
50
40
30
20
Diluate
10
0
0
76
60
120
180
240
300
360
420
480
Time (min)
Fig. 5. The time course of the three-level desalting
electrodialysis experiment (membrane stack ED 0,
fermentation broth)
Czech J. Food Sci.
Vol. 19, No. 2: 73–80
Table 1. Desalting electrodialysis experiments
Experiment
Operating
time
Switching
time
Concentration
initial diluate
final diluate
final concentrate
VD0/VK0
Water transport
index
(min)
(min)
(g/l)
(g/l)
(g/l)
DS 1
acf
360
240
41.2
1.6
37.5
1.00
(ml/g)
4.25
DS 2
acg
330
180
39.8
1.7
36.4
1.00
4.50
DS 3
ac
300
150
39.8
1.9
35.8
1.00
4.53
DS 4
ac
600
290
37.4
2.0
54.9
1.95
5.06
DS 5
ac
690
270
34.9
2.3
76.6
3.73
5.54
DS 6
ac
1020
480
42.5
2.1
111.2
5.09
4.74
DS 7
bc
80
50
43.7
0.8
34.1
1.00
7.08
DS 8
bc
160
100
39.6
0.8
52.6
1.87
5.27
DS 9
bch
150
100
42.4
1.2
61.5
1.87
4.71
DS 10
bck
100
100
40.4
1.2
55.9
1.87
5.20
DS 11
bc
75
15
15.3
0.7
26.9
1.87
4.78
DS 12
bd
120
40
18.4
1.3
29.2
1.87
6.97
DS 13
bd
165
50
17.3
1.3
45.4
1.87
9.04
DS 14
bd
195
70
22.2
1.2
60.6
1.87
9.10
Lactate
transport
Rate
of lactate
transport
Current
efficiency
Energy
consumption
Constant-current period
rate of lactate
transport
current
efficiency
energy
consumption
(g)
(g/h)
(%)
(kWh/kg)
(g/h)
(%)
DS 1
82.4
13.7
80
0.61
17.2
81
(kWh/kg)
0.60
DS 2
80.0
14.6
79
0.73
21.1
83
0.71
DS 3
79.5
15.9
78
0.79
23.8
80
0.82
DS 4
144.3
14.4
73
0.81
22.2
75
0.83
DS 5
130.9
11.4
65
0.90
21.2
71
0.87
DS 6
221.4
13.0
68
0.84
21.6
73
0.81
DS 7
83.3
62.5
68
0.34
79.6
67
0.35
DS 8
161.2
60.4
66
0.31
77.7
65
0.32
DS 9
180.3
72.1
74
0.27
91.1
77
0.26
DS 10
167.3
60.8
60
0.32
67.0
56
0.34
DS 11
60.7
48.6
76
0.29
80.8
68
0.40
DS 12
73.2
36.6
54
0.41
58.6
53
0.45
DS 13
67.5
24.6
42
0.54
53.1
45
0.56
DS 14
90.1
27.7
44
0.48
53.4
45
0.48
a stack Type 500; b stack ED 0; c model solutions of lactate; d fermentation broth; f current 1 A; gcurrent 1.2 A; h addition of glucose to
the diluate (9 g/l); kaddition of glucose (9 g/l) and salts (K2HPO4, MgSO 4, MnSO4, sodium acetate, ammonium citrate) to the diluate;
V D0 /VK0 ratio of the initial diluate volume to the concentrate volume
transport rate decreased with a higher ratio of initial volumes. In the course of electrodialysis experiments the concentrate and diluate volumes changed due to water
passage by electroosmosis through the membranes simultaneously with lactate ions. Water transport index
(amount of passed water to amount of transported lactate) was in the range from 4.3 to 5.5 ml/g (stack Type 500)
and from 4.8 to 7.1 ml/g (stack ED 0) in our experiments.
The influence of other components (glucose and salts,
which are commonly present in the fermentation broth)
on electrodialysis (see the legend to Table 1) was studied.
While the addition of glucose to the diluate did not show
any effect, the addition of salts resulted in a decrease in
current efficiency. The current efficiency was in the range
from 60% to 80% during the electrodialysis experiments
with the model solutions and the energy consumption
77
Vol. 19, No. 2: 73–80
Czech J. Food Sci.
4
Current
16
12
Voltage
8
Conductivity
4
0
2
Fig. 6. The time course of the water-splitting electrodialysis experiment (WS 1)
1
0
0
10
20
30
40
50
60
70
80
Time (min)
35
Concentration (g/l)
3
Current (A)
Conductivity (mS/cm)
Voltage (V)
20
30
25
Lactic acid
20
15
10
NaOH
5
0
0
10
20
30
40
50
60
70
80
Time (min)
was from 0.6 to 0.9 kWh/kg (stack Type 500) and 0.3 kWh/
kg (stack ED 0). The electrodialysis experiments with the
pre-treatment of fermentation broth were carried out. The
fermentation broth pre-treatment was carried out to prevent a decrease in electrodialysis efficiency due to the
colour fixing on the membrane surface (HERIBAN 1993).
The comparison of the lactate recovery from the model
solutions (DS 11) and from the fermentation broth (DS 12)
has shown that in the case fermentation broth the transport rate decreased by 25%. The energy consumption increased and the current efficiency decreased. The other
components that are present in the fermentation broth
were probably transported through the membranes together with lactate. Fig. 4 shows the time course of the
three-level electrodialysis with fermentation broth when
231 g lactate was transported from the diluate to the con-
centrate. About 94% of the total amount of lactate present
in the diluate was recovered. About 1 g lactate per litre
remained in the diluate after each level. The concentration of lactate obtained during the three-level electrodialysis was about 3 times higher than the lactate
concentration in the fermentation broth.
Water-splitting Electrodialysis
Water-splitting electrodialysis was the second recovery step, when sodium lactate was converted to lactic
acid. Fig. 6 shows an example of water-splitting experiment (WS 1). It is obvious that the experiments were carried out at constant fixed current (3.9 A), which was higher
than that during desalting electrodialysis. The results of
two water-splitting experiments (Table 2) indicate that
the amount of converted sodium lactate is proportional to
Table 2. Water-splitting experiments
Experiment
Operating
time
(min)
Initial diluate
concentration
(g/l)
Final diluate
concentration
(g/l)
Final concentrate
concentration
(g/l)
Na+ transport
(g)
WS 1
82.5
43.3
29.7
14
15.9
WS 2
406.0
178.3
156.8
58
70.8
lactic acid conversion
(g/h)
Current
efficiency
(%)
Experiment
Water
transport index
(ml/g)
Rate of
+
Na transport
(g/h)
Energy
consumption
(kWh/kg)
WS 1
0.0038
11.6
45.3
92
0.91
WS 2
0.0030
10.5
41.0
78
0.84
78
Czech J. Food Sci.
Vol. 19, No. 2: 73–80
Absorbancy at 400nm
0.35
300 ml/h
0.30
Fig. 7. Decolourisation of fermentation broth
at different flow rates
0.25
0.20
120 ml/h
0.15
40 ml/h
0.10
0.05
0.00
0
4
8
12
16
20
24
Bed volumes
the amount of supplied charge. High current efficiency
80–90% was achieved. The energy consumption of water-splitting electrodialysis has increased in comparison
with desalting electrodialysis, from 63 to 79 Wh/mol. The
results confirmed the possibility of sodium lactate conversion to lactic acid with the use of water-splitting electrodialysis with bipolar membranes.
Decolourisation
Due to high demands of the electrodialysis membranes,
esp. water-splitting ones, for the quality of solutions used
in electrodialysis processes, the fermentation broth had
to be decolourised. Two decolourising agents were tested. Granulated active charcoal showed the higher decolourisation capacity than Amberlite resin. Further
experiments were carried out with active charcoal only.
The flow of the fermentation broth through the column
significantly influenced the decolourisation degree. The
course of decolourisation experiments at different flow
rates is shown in Fig.7. When the flow rate was only
40 ml/h, the amount of fermentation broth corresponding
to the 10-fold bed volume was decolourised from 90%.
When the decolourisation was carried out in a batch mode,
decolourisation degree was equal to that mentioned above,
but more decolourising agents were consumed.
CONCLUSION
The obtained results confirm that two-stage electrodialysis is a suitable and efficient technique for recovery of
lactate ions from the pre-treated fermentation broth and
subsequent conversion into lactic acid with respect to
environmental aspects.
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Received for publication November 30, 2000
Accepted for publication February 1, 2000
Souhrn
HÁBOVÁ V., MELZOCH K., RYCHTERA M., PØIBYL L., MEJTA V. (2001): Využití elektrodialýzy pro izolaci kyseliny
mléèné. Czech J. Food Sci., 19: 73–80.
Práce se zabývá využitím dvoustupòové elektrodialýzy pro izolaci kyseliny mléèné z modelových roztokù a fermentaèního
média. V prvním stupni byl laktát sodný nakoncentrován pomocí elektrodialýzy s iontomìnièovými membránami Ralex.V 1 l
koncentrátu bylo získáno až 111g laktátu sodného, tzn., že koncentrace se ve srovnání s pùvodní hodnotou zvýšila více než
2,5krát, v diluátu zùstávalo nejvýše 2 g laktátu v 1 litru. Ve druhém stupni byl laktát sodný pomocí elektrodialýzy s bipolárními
membránami Neosepta konvertován na kyselinu mléènou – v 1 l diluátu bylo 157 g kyseliny mléèné. Na izolaci (tj. na koncentrování
a na elektrokonverzi) kyseliny mléèné bylo zapotøebí celkem 142 kWh/mol. Reálná fermentaèní média byla pøed elektrodialyzaèními
pokusy odbarvována. Nejlepších výsledkù bylo dosaženo s granulovaným aktivním uhlím v kolonì s nízkým prùtokem.
Klíèová slova: izolace kyseliny mléèné; elektrodialýza; odsolovací elektrodialýza; elektrodialýza s bipolárními membránami;
odbarvování
Corresponding author:
Doc. Ing. KAREL MELZOCH, CSc., Vysoká škola chemicko-technologická, Ústav kvasné chemie a bioinženýrství, Technická 5,
166 28 Praha 6, Czech Republic, tel.: +420 2 24 35 41 27, fax: +420 2 24 35 50 51, e-mail: [email protected]
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